1. Field of the Invention
The present invention relates to an apparatus and a method for signal processing in a digital video system, and more particularly, to an apparatus and a method for signal processing in a digital video system capable of displaying with a lesser number of bits and minimizing the loss of an image signal quantized with a greater number of bits. The present application is based on Korean Patent Application No. 2002-40599, which is incorporated herein by reference.
2. Description of the Prior Art
In a digital video system like a DTV (digital TV), an A/D conversion (analog to digital conversion) process to digital code an analog input signal is required in order to display an image on a screen.
The A/D conversion process is used to convert a continuously changing analog image or an audio signal into a discrete digital signal. A sampling frequency and quantization bit number in the A/D conversion process influence the quality of a picture and sound, and the amount of information of the digital video system. In other words, as the sampling frequency increases, a higher band frequency can be reproduced. Thus, the quality of the picture and sound can be upgraded. Yet, the amount of information for transmission and recording also increases in proportion to the sampling frequency.
Similarly, the quantization bit number for one sample influences the quality of picture and sound, and the amount of information. For example, a mosaic screen frequently used for protecting one's portrait is very coarse and the content of the mosaic is actually difficult to recognize, since the quantization bit number is set up to be very low in digital signal processing. Unlike the above case, when the quantization bit number is increased, quantization stem width is reduced and the quality of picture and sound is improved. Yet, the amount of information is increased in proportion to the quantization bit number like the case of the sampling frequency. Thus, it is difficult to increase the number without a plan.
Due to the above technical limitation, audio systems having a lesser amount of information were digitalized before video systems, and the sampling frequency and the quantization bit number of a CD, which is a representative digital audio system are individually 44.1 kHz and 16 bits, respectively. In the case of a motion picture signal having 200 times more reproducing bandwidth than an audio signal, when the quantization bit number is more than 16 bits, the amount of information is astronomically increased. Thus, it is realistically impossible to convert and record an image signal into a digital code. Therefore, the quantization bit number of the digital video system should be decided considering economical efficiency, visual characteristics of people and the quality of picture that has no practical problem in subjective evaluation that can be judged from a real screen. Generally, 8 bits or 10 bits are used for the quantization bit number, and recently, a digital processor camera of 12 bits has been introduced.
The resolution of 8 bits has a maximum level of 28 (=256), that of 10 bits has a maximum level of 210 (=1024) and that of 12 bit has a maximum level of 212 (=4096). Accordingly, an 8 bit system has a much lesser amount of information and the quantization stem is coarse compared to a 10 bit system. On the other hand, an 8 bit system has a longer quantization stem width than a 10 bit system. Thus, it is difficult for an 8 bit system to describe a slant object such as an oblique line or an arc in detail like the analog system does.
Accordingly, to obtain good quality of picture and sound in the digital video system, the quantization bit number should be increased, but the circuit structure for processing the increased amount of information is complicated, and the price for the product is also increased.
For the above reasons, the digital video system generally applies 8 bits for the quantization bit number, and in this case, the 8 bits are used not only for the quantization bit number but also for a luminance signal (Y) or a chrominance signal (Cb, Cr) for expressing a picture element or a pixel that is a composition element corresponding to one dot in a screen. In other words, in an 8 bit digital video system, even though an image signal input in the A/D conversion process is quantized for more than 10 bits, the low 2 bits are ignored and only the remaining 8 bits are used to display an image on a screen.
However, the realization of quantization of more than 8 bits in the A/D conversion process is easy thanks to technical development, and thus the price of a product is lowered. On the other hand, to increase quantization level more than 8 bits for a luminance (Y) or chrominance signal (Cb, Cr) for expressing a pixel is a relatively difficult matter in realization of a circuit or the price.
Accordingly, in the digital video system, an apparatus and a method for signal processing capable of improving the quality of a picture by reflecting discarded low bits is required when low bits are discarded at quantized data and only the high 8 bits are used to display a screen in the case that an image signal input in the A/D conversion process can be quantized to more than 10 bits.